Effect of combined application of heat treatments and plastic packaging on keeping quality of ‘Oroblanco’ fruit (Citrus grandis L.×C. paradisi Macf.)

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Abstract

Combinations of various heat treatments with individual fruit sealing, packaging in polyethylene liners or waxing were tested as means to control pathological and physiological spoilage of ‘Oroblanco’ fruit (Citrus grandis L.×C. paradisi Macf.). The following heat treatments were used: curing at 36°C for 72 h, hot water dip at 52°C for 2 min or ‘hot drench brushing’ at 52, 56 or 60°C for 10 s. The standard packinghouse treatment included waxing with addition of thiabendazole (TBZ) and 2,4-d isopropyl ester. The fruit was stored for 2 weeks at 1°C (simulated low-temperature quarantine treatment), followed by 12–13 weeks at 11°C (simulated sea transportation to Japan) and 1 additional week at 20°C (simulated retail shelf-life period). The lowest weight loss and the highest firmness were observed with individually sealed fruit. Polyethylene liners were usually more efficient for weight loss control than waxing. However, the liner packaging enhanced the risk of postharvest disease development, if not accompanied by appropriate decay-controlling measures. Applying TBZ, hot water dip or curing controlled the development of postharvest pathogens, especially that of Penicillium molds. In another trial, both hot drench brushing at 56 or 60°C and hot water dip reduced decay incidence. Hot drench brushing at 60°C and hot water dip slowed fruit softening and reduced buttons abscission. In addition, the hot drench brushing at 60°C significantly delayed the loss of ‘Oroblanco’ green rind color, especially at the stylar and stem ends of the fruit. The hot dip at 52°C inhibited yellowing only when combined with individual seal-packaging.

Introduction

‘Oroblanco’ citrus, known also under the commercial name ‘Sweety’, is a triploid pummelo-grapefruit hybrid. This variety retains green rind color far longer than grapefruit and has noticeably sweeter flavor related to higher sugar content, lower acidity and lack of bitterness (Soost and Cameron, 1981).

Export of ‘Oroblanco’ to Japan requires a low-temperature quarantine treatment against the Mediterranean fruit fly. The marine transportation to the Far East markets can take 8–12 weeks. ‘Oroblanco’ fruit spoilage is caused primarily by Penicillium digitatum Sacc. and P. italicum Wehmer (green and blue mold diseases, respectively), and physiological deterioration, such as loss of typical green rind color, desiccation and chilling injury.

Heat treatments are promising non-chemical means to control fruit pathogens. Postharvest curing at 34–36°C for 48–72 h effectively controls citrus decay and reduces chilling injury symptoms (Ben-Yehoshua et al., 1987, Del Rio et al., 1992). Shrunk seal-packaging in plastic film is essential during curing to reduce water loss from the fruit and thus protect it from high temperature damage (Ben-Yehoshua et al., 1987). However, practical implementation of curing is complicated by its long duration. Application of relatively short-term hot water dips (2–3 min at 50–53°C) also reduces disease susceptibility and sensitivity to suboptimal storage temperatures of various citrus fruits, including ‘Oroblanco’ (Schirra and Mulas, 1993, Rodov et al., 1995). The ‘hot drench brushing’ technique including hot water drench (10–30 s at 55–64°C) in combination with brushing (Israeli patent 116965) is commercially used in Israel with bell peppers (Fallik et al., 1999), mangoes (Prusky et al., 1999), kumquat (Ben-Yehoshua et al., 1998) and several other crops to reduce decay.

The objective of the present work was to test various heat treatments in combination with several methods of weight loss reduction as non-chemical means to control pathological and physiological spoilage of the ‘Oroblanco’ fruit during simulated shipment to Japan. The efficacy of these treatments was compared with chemical treatments currently used in citrus packinghouses.

Section snippets

Materials and methods

‘Oroblanco’ fruit were obtained on the day of harvest from the packinghouse in HaSharon valley (Israel) before any treatment was applied (unless specified otherwise) and divided into three lots of 240 fruit each.

The fruit of one lot were dipped in hot water (2 min at 52°C) and after air-drying either individually sealed, or packaged in cartons with perforated polyethylene liners, or waxed with Zivdar water wax (Safe-Pack Co, Kfar Saba, Israel). The 19 μ thick Cryovac MD polyolefin (Cryovac

Weight loss

Waxing, individual sealing and use of polyethylene liners significantly inhibited weight loss of fruit during prolonged storage. Individual sealing provided the best weight loss control. Perforated polyethylene liners were more effective than waxing for weight loss reduction, except for the combination of liners with curing (Fig. 1A). The increase of weight loss from liner-packaged and cured fruit could occur during their 3-day incubation at high temperature due to the presence of perforations

Discussion

The results demonstrate that combining heat treatments and plastic packaging may protect ‘Oroblanco’ fruit against decay and desiccation similar to chemicals (fungicides+waxing). Since curing and hot water dip showed close efficacy, hot water dip may have certain practical advantage as a shorter treatment (Rodov et al., 1995). However, up-scaling of the hot dip method from the laboratory to packinghouse scale demands additional technical solutions to maintain a desired treatment regime with

Acknowledgements

Contribution No 422/99 from the Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel. This work was partially supported by the Citrus Marketing Board of Israel and by the scholarship of the Department of International Cooperation of the Ministry of Foreign Affairs of Israel given to Tayfun Agar. We are grateful to the authors of hot drench brushing technique (E. Fallik, O. Yekutieli, A. Wiseblum and R. Regev) for providing the opportunity to test the performance of this

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